ikiwiki also has an older syntax for directives, which requires a space in
directives to distinguish them from wikilinks. This
syntax has several disadvantages: it requires a space after directives with
no parameters (such as [[pagecount ]]), and it prohibits spaces in
wikilinks. ikiwiki now provides the !-prefixed
syntax shown above as default. However, ikiwiki still supports wikis using
the older syntax, if the prefix_directives option is disabled.